Fluid extrusion dies are used in manufacturing processes to make a variety of goods. Some dies, for example, are used to form thin films, bars or other elongated shapes of plastic material. Other dies are used to apply a coating of fluent material to a moving web. A number of different coating dies have been constructed to apply a liquid or semi-liquid material to a moving web. In general, such dies receive the liquid or semi-liquid material under pressure from a pump or other device, and distribute the material to regions across the width of the web as the web is advanced in directions along its longitudinal axis.
Many conventional dies have an inlet passageway, an outlet passageway and an inner cavity that extends between the inlet passageway and the outlet passageway. The outlet passageway is relatively wide and often approximates the width of the web in instances where the die has a slot-type outlet for discharging a ribbon of fluid onto the web. The inner cavity is also relatively wide, and serves as a manifold to distribute incoming fluid from the inlet passageway to various regions of the outlet passageway.
Some coating dies, known as slot dies, include an outlet passageway in the form of a transverse slot that discharges the fluid material in a sheet-like bead on a continuous substrate or web. A typical slot coating die has an internal cavity that is used to distribute liquid across the width of a moving web such that it can be uniformly coated with the liquid. The profile of the cavity is chosen to provide the necessary cross-web uniformity for a range of liquids and desired feed rates used in production of coated articles. Similarly, the width of the cavity is chosen so that the die is able to coat the widest webs that can be threaded through the coater head.
For some coating applications it is desirable to use the central portion of the slot to distribute liquid as a strip across a narrower width of a wider substrate web or alternatively, across the entire width of a web that is appreciably narrower than the nominal width of the die. In such cases, the effective width of the slot can be reduced with additional deckles or a cut shim positioned across the slot. Partial or full die inserts can also be used to reduce the effective slot width.